For years, flavour additives in e-cigarettes have been largely viewed as a secondary concern compared with nicotine. Research and regulation have focused on addiction, nicotine delivery and, more recently, the respiratory effects of vaping. But as evidence accumulates researchers are increasingly asking whether certain flavouring ingredients have health effects of their own.

Among the compounds attracting attention are menthol and synthetic cooling agents that create the refreshing sensation associated with popular “ice” flavours. These additives now appear in everything from mint-flavoured products to fruit and confectionery blends – and research suggests they may be doing more than simply enhancing the vaping experience.

The cooling sensation is often created by menthol or menthol-inspired synthetic compounds such as WS-3 and WS-23. These substances do not........

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